It is broadly known to employ poly(arylene sulfide) compositions as coatings for a variety of substrate materials including iron-containing alloys such as steels of various types. Various methods are also known for applying the coating compositions which comprise the arylene sulfide polymers. Generally, the above-described coatings are subjected to a curing step prior to use of the coated substrate in the intended application.
In spite of the generally very good results obtained with the poly(arylene sulfide) coating compositions and methods of the prior art, it has been found that these known compositions and methods sometimes give unsatisfactory results when the coated substrate is employed under the harsh conditions which may include elevated temperatures, e.g. about 40.degree. to about 125.degree. C., and corrosive environments such as hydrogen sulfide, brines, carbon dioxide, and the like. Under such conditions the known arylene sulfide polymer coatings may fail catastrophically, e.g. peel off in large areas, or the underlying substrate may corrode rapidly around microscopically small defects in the coating. Such defects are frequently referred to as pinhole defects or holidays. In either case the coating has failed to protect the substrate and loss results from the failure of the coating. Attempts to employ alternative polymeric coatings under the harsh conditions described above have not proven to be satisfactory for a variety of reasons such as high materials cost and short lifetime due to failures of the same type as noted above.
Though we are not bound to any extent by the following theory, it is currently believed that the failure of arylene sulfide polymer coatings under the harsh conditions described above is primarily due to the presence of one or more exposed areas of substrate. Usually, these will be the pinhole defects that are difficult to observe even under a microscope. Nevertheless, the harsh environment attacks the substrate at such exposed areas with often devastating results. An apparent solution to the problem would be to use the known technique of multiple applications of the coating composition to the substrate. While this procedure has been somewhat effective, it has been found that the number of applications, using the conventionally employed arylene sulfide polymers, becomes prohibitively large and the coating often unacceptably thick to achieve a coated substrate substantially free of exposed substrate, e.g. pinhole defects.
Thus there is a need for poly(arylene sulfide) coating compositions and methods of application which will provide an adherent, corrosion resistant, relatively thin coating substantially free of pinhole defects which can be easily applied and which can withstand the harsh environment conditions described above.
It is therefore an object of this invention to provide coatings comprising at least one arylene sulfide polymer suitable for a variety of substrates which are adherent to said substrates, hard (abrasion resistant), corrosion resistant and substantially free of pinhole defects.
It is another object of this invention to provide a method of coating a variety of substrates with compositions comprising at least one arylene sulfide polymer which is simple to carry out and which produces an adherent, hard, corrosion resistant, relatively thin coating substantially free of pinhole defects.
It is another object of this invention to provide powdered and liquid slurry coating formulations comprising at least one arylene sulfide polymer which can be utilized in a variety of methods to coat a variety of substrates to obtain adherent, hard, corrosion resistant coatings substantially free of pinhole defects.
It is yet another object of this invention to provide well pumping tools and equipment such as sucker rods and tubing having a coating on at least one surface thereof wherein said coating comprises at least one arylene sulfide polymer and is adherent, hard, corrosion resistant, and substantially free of pinhole defects.